system design · interview loop

Practice the interview, until the reasoning is automatic.

FOUNDATIONS · COMPONENTS · PATTERNS · SYSTEMS · INTERVIEW

from fundamentals to mock interview pressure

RunDrill plays the interviewer, pushes on weak tradeoffs, scores the answer, and brings the same gaps back until they stop leaking.

Install the coach See the loop

Free while in beta · works inside Claude, Codex, Antigravity, and any MCP client.

Example

C Claude RunDrill System design

C

Review this design for a read-heavy timeline. What breaks first?

APIstateless

Single DBall reads

Cacheoptional

Writerfan-in

Queueasync

Workersbatch

The DB is a single read bottleneck and probably a SPOF.

C

Good. Now defend a fix: cache, read replicas, fan-out, or a different data model? Pick one and name the tradeoff.

Tracked — bottleneck reasoning

C

You chose cache-aside. The interviewer pushes: stale data is unacceptable for this feature. What changes?

Keep the design, change the consistency path, and explain the cost.

Then writes should invalidate synchronously, or this feature bypasses cache.

C

That is the right direction. Name the latency and availability cost, then we can score it.

C

Debrief. Your design passed the basic shape, but depth was thin around cache invalidation.

Problem navigationE5

Solution designE4+

Technical depthE4

CommunicationE5

Next drill — cache invalidation

01 — why this works

Not answer memorization.
Interview reasoning under pressure

Find the hidden flaw

Review plausible designs with planted defects: hot shards, lying caches, unbounded queues, wrong consistency, or one critical service with no backup.

Defend tradeoffs

The coach pushes back like an interviewer. You commit, explain what you gain, name what you lose, and adapt when the requirement changes.

Practice the math

Back-of-envelope estimates become short drills, not a vague interview ritual. You learn when the estimate changes the architecture.

Know your level

Mock interviews end with a scorecard across problem navigation, solution design, technical excellence, and communication.

02 — inside the course

Ninety tracked topics,
from load balancers to full systems

The course climbs five bands: foundations, components, patterns, complete system designs, and interview execution. Each miss becomes future practice instead of disappearing into chat history.

FOUND01

Scaling fundamentals

Latency, throughput, load balancing, stateless services, CAP, and the first bottlenecks that appear under traffic.

concepts / estimation

COMP24

Core components

SQL and NoSQL, indexes, replication, sharding, caches, queues, streams, object storage, search, APIs, and WebSockets.

components / tradeoffs

SYS23

Full system prompts

Design rate limiters, feeds, chat, video, ticketing, search autocomplete, payments, collaborative editing, cloud storage, and more.

systems / deep dive

INT08

Interview execution

Clarify requirements, estimate capacity, draw the high-level design, choose deep dives, discuss tradeoffs, and close cleanly.

mock / level read

03 — the mock loop

What happens in a session

A session is not a lecture. The coach asks one thing, waits for your answer, then probes the weak spot before revealing the stronger version.

01

Status first

It reads your current level, open mistakes, target track, and recent weak spots before picking the next drill.

02

Struggle before reveal

You clarify, estimate, critique, design, or defend first. The coach does not hand you the architecture before you try.

03

Debrief with a model answer

If the answer was hard, the close includes a compact ideal answer so you can see the shape: scope, architecture, tradeoffs, bottleneck, and next deep dive.

scorecard

Today’s gap: you named components but did not say which requirement each one protects.

BreadthE5

DepthE4

ProactivenessE4+

Next: defend consistency choice

04 — start

Install the coach

Add the RunDrill marketplace, install the system-design plugin, then start the coach inside the agent where you already work.

Type these straight into Claude Code or Claude Desktop:

# add the marketplace, then the course
/plugin marketplace add rundrill/rundrill
/plugin install rundrill-system-design@rundrill

# then start coaching
/system-design-coach

Add the RunDrill catalog, then install from the plugin directory:

codex plugin marketplace add rundrill/rundrill

Install rundrill-system-design, then start the system-design-coach skill.

Drop the rundrill-system-design folder into one of these:

# for every project
~/.gemini/config/plugins/rundrill-system-design/

# just this workspace
<workspace>/.agents/plugins/rundrill-system-design/

Restart the agent and start the system-design coach.

Any MCP client can point directly at the coach endpoint:

{
  "mcpServers": {
    "rundrill-system-design": {
      "type": "http",
      "url": "https://mcp.rundrill.com/coach/system-design"
    }
  }
}

First run opens a browser tab to sign in once. Your progress lives on the RunDrill server, so weak spots follow you across chats and machines.

part of rundrill

System Design is one of the RunDrill programs — languages, programming, interview prep, and exam prep, all inside your agent.

See all programs